求指导一个实现三级下拉框的Jquery或Ajax脚本（已有JSON数据）

求指点一个实现三级下拉框的Jquery或Ajax脚本（已有JSON数据）
JSON数据示例：

[

    {

        "reports": [

            {

                "companies": [

                    {

                        "companyName": "company1"

                    }, 

                    {

                        "companyName": "company2"

                    }

                ], 

                "rptName": "rpt1"

            }, 

            {

                "companies": [

                    {

                        "companyName": "company1"

                    }, 

                    {

                        "companyName": "company2"

                    }

                ], 

                "rptName": "rpt2"

            }

        ], 

        "typeName": "type1"

    }, 

    {

        "reports": [

            {

                "companies": [

                    {

                        "companyName": "company1"

                    }, 

                    {

                        "companyName": "company2"

                    }

                ], 

                "rptName": "rpt1"

            }, 

            {

                "companies": [

                    {

                        "companyName": "company1"

                    }, 

                    {

                        "companyName": "company2"

                    }

                ], 

                "rptName": "rpt2"

            }

        ], 

        "typeName": "type2"